Wind mark definition
Generally refers to a dyeing defect produced during the drying and storage process of printed and dyed textiles.
Compared with the normal dyed light base, the wind-stamped area will show white or dull gray long strips in the latitudinal direction of almost the entire door width. This defect is not visible before setting, but will appear after setting.
Polyester fabrics are not prone to wind marks during continuous production (long car production lines), but are prone to wind marks during intermittent production (high temperature and high pressure overflow dyeing).
Most of the wind marks on polyester fabrics occur after the fabric is dehydrated and opened and before it is set, and appear in the reciprocating folding marks when the fabric is stored in the stacker. In severe cases, dozens of strips will appear in the weft direction, and their spacing is exactly the spacing of the reciprocating folding of the gray fabric.
The reason why sizing-free polyester woven fabrics or knitted fabrics produce wind marks
During the process of placing such fabrics after opening, the reciprocating folds are exposed to the air, and the flow of air causes The moisture in these parts evaporates first and is air-dried. Due to the capillary effect, free water in other parts will flow towards the reciprocating folds.
However, antistatic agents, lubricants added during spinning and weaving, and leveling agents, detergents, etc. added during post-dyeing processing will still have a small amount of residues in the fabric and the free water carried by the fabric. , and most of these additives are nonionic additives. Similar to the principle of dye migration, when free water flows to the reciprocating folding point, the residual additives dissolved in the free water also flow to the reciprocating folding point.
As the water evaporates further, the concentration of additives in the reciprocating folds is much greater than in other parts. During the high-temperature setting process, the thermal migration of disperse dyes produced in the reciprocating folding parts is significantly greater than that in other parts.
The reason for the thermal migration of disperse dyes is that the additives in the outer layer of the fiber can dissolve at high temperatures. The dye migrates from the inside of the fiber to the surface of the fiber through capillaries, causing the dye to accumulate on the surface of the fiber, causing a series of effects. . Such as color change, friction, washing, sweat stains, dry cleaning, light fastness and other color fastness decreases.
But the fatal impact is the serious color difference between the reciprocating fold and other normal parts, that is, the wind mark.
The reason why sizing polyester woven fabrics produce wind marks
Compared with sizeless polyester woven fabrics or knitted fabrics, the dyeing and finishing of sizing polyester woven fabrics is The process takes a long time, and most of the additives used in spinning and weaving have been removed. However, small amounts of the auxiliaries used during dyeing and post-processing may still remain in the fabric and the free water it carries.
In addition, although it has been hot washed twice and pickled once after desizing, a small amount of caustic soda used during desizing may still remain inside the single fibers of the polyester fiber and even inside the amorphous zone. .
Similarly, during the process of stacking fabrics before they are finalized, free water can carry residual alkali and additives and flow to the reciprocating folds. At this time, the pH value of the reciprocating folds is significantly higher than that of other parts of the fabric. This has also been confirmed by using a universal indicator, and the concentration of the additive is also greater than that of other parts. During the high-temperature setting process of fabrics, polyester macromolecular chains move violently, and OH- ions can instantly penetrate into the amorphous zone with water molecules to react with disperse dyes.
Disperse dyes are relatively stable under acidic conditions (pH value 5). Alkaline conditions generally have the following two effects on disperse dyes:
Alkaline conditions can cause certain dyes to Structural dissociation, this reaction is reversible, and the undissociated structure will reappear in a neutral or slightly acidic structure.
Alkali can hydrolyze certain disperse dyes. After hydrolysis, the dyes not only change their color and light, but also have different affinities. Therefore, alkali can permanently damage some disperse dyes.
Therefore, the discoloration at the reciprocating folds of sized polyester woven fabrics is caused by excessive pH value, hydrolysis or dissociation of disperse dyes, and the combined effect of thermal migration of disperse dyes by additives.
Methods to avoid wind marks on polyester fabrics
If the above two fabrics can be dehydrated, opened and shaped in time after coming out of the vat, generally they will not Wind marks will be produced. If left for a period of time (about 30 hours) before shaping, it is easy to produce wind marks. In order to fundamentally solve the problem of wind marks, we must start from the mechanism of wind marks and reduce the factors that cause wind marks to a minimum.
It is found that there are wind marks after setting, and the high concentration of additives or OH-ions in the reciprocating folds of the remaining unshaped fabric are only physically adsorbed on the fiber surface and cannot be dissolved without high-temperature setting aids. The dyes in the fiber region, OH- ions cannot enter the amorphous region of the fiber to react with disperse dyes. Therefore, after water washing or pickling, the high concentration of additives and OH-ion ions in the reciprocating folds have been diluted, and re-shaping in time can avoid wind marks. </p
